This invention relates to processes for making isocyanatosilanes and 1,3,5-tris[(trialkoxysilyl)alkyl]isocyanurates.
A variety of processes are known for making isocyanatosilanes.
U.S. Pat. Nos. 3,494,951 and 3,607,901 describe processes for making isocyanatosilanes by the pyrolysis (cracking) of silylorganocarbamates.
According to the process described in U.S. Pat. No. 5,393,910, silylorganocarbamate is vaporized in a reaction zone at elevated temperature, e.g., between 300° C. and 600° C., to form an isocyanatosilane.
U.S. Pat. No. 6,008,396 discloses the so-called “hot oil” process for making isocyanatosilanes. In accordance with this process, a carbamatoorganosilane (i.e., a silylorganocarbamate) is added to an inert liquid medium and the mixture thus formed is held at a temperature and pressure effective to convert the carbamatoorganosilane to isocyanatosilane.
U.S. Pat. No. 6,388,117 describes a process of catalytically cleaving (cracking) a carbamatoorganosilane (i.e., a silylorganocarbamate) in the liquid phase to provide isocyanatosilane employing a cleavage and distillation reactor. A portion of the reaction medium, e.g., 15-25 weight percent, is purged from the bottom of the reactor in order to keep high molecular weight components at a constant level. The purged material is then allowed to mix with alcohol to quench the isocyanatosilane, is redistilled and a portion thereof is reintroduced to the reactor.
High temperature vapor phase processes for making isocyanatosilanes are described in U.S. Pat. No. 5,393,910 and U.S. Patent Application Publication Nos. 2004/0049064 and 2004/0249179. These processes suffer from the requirement for specialized equipment capable of high temperature operation with their concomitantly high capital investment requirements.
DE 10161272 describes a process wherein a silylorganocarbamate is cracked in the presence of a high molecular weight isocyanate and transition metal catalyst.
JP 09328489 describes a process where 3-aminopropylsilane is first reacted with isocyanate such as MDI to provide the corresponding urea which is then thermally cracked in the presence of catalyst to provide isocyanatosilane.
A number of processes for making isocyanatosilanes utilize low temperature cracking of a carbamate derivative.
U.S. Pat. No. 4,697,009 describes a process for making isocyanatosilane wherein an acyl-urea group is utilized as the leaving group rather than alkyl alcohols which are most common. This process suffers from the intermediate preparation that involves difficult separation of solvent and the resulting salt.
U.S. Pat. No. 4,064,151 discloses the preparation of isocyanatosilane by preparing a halosilyl carbamate by direct reaction of aminosilane in the presence of carbon dioxide and halosilyl compounds and a tertiary amine acid scavenger. The resulting halosilyl carbamate decomposes at a relatively low temperature to yield the isocyanatosilane. A difficult workup is required to obtain the product.
DE 10,108,543 describes a process where silylorganocarbamate is reacted directly with methyl trichlorosilane to provide N-silylated carbamate which then decomposes under slight heating to provide isocyanatosilane and an equimolar amount of alkoxychloromethylsilane. This method suffers from the requirement of an acid trap such as triethylamine which then requires separation and disposal or recycle.
Typical of non-cracking methods for making isocyanatosilanes are those described in JP 09208589 and U.S. Pat. No. 4,654,428 in which an aminopropylsilane is directly reacted with highly toxic phosgene to yield the desired isocyanate.
There are a number of known processes for making silylisocyanurates.
U.S. Pat. No. 3,598,852 describes a process for making silylisocyanurate in which a haloorganosilane intermediate is reacted with a metal cyanate in the presence of a high boiling polar solvent such as dimethylformamide. Subsequently, the polar solvent is removed by vacuum stripping. However, the solvent is toxic and difficult to remove.
U.S. Pat. No. 4,880,927 describes a process for preparing silylisocyanurate in which the silylisocyanate is thermally treated or heated for cyclization to the trimer in the presence of a strongly basic catalyst such as an alkali metal hydroxide or alkoxide. However, when this process is employed for the preparation of silylisocyanurate, it requires the isolation of toxic isocyanate and results in a highly colored product.
U.S. Pat. No. 5,218,133 describes the cracking of silylorganocarbamate in the presence of cracking catalyst under moderate heating and subatmospheric pressure to a non-isolated isocyanatosilane intermediate and by-product alcohol, the isocyanatosilane then undergoing trimerization in the presence of trimerization catalyst in situ to provide silylisocyanurate. Typical cracking catalysts for this process include aluminum, titanium, magnesium and zirconium alkoxides such as aluminum triethoxide which is indicated to be preferred and tin carboxylates such as dibutyltin dilaurate, dibutyltin diacetate and stannous octoate which are indicated to be preferred. Trimerization catalysts employed in the process of U.S. Pat. No. 5,218,133 include sodium methoxide and the alkali metal salts of organic acids such as the sodium, potassium, lithium and cesium salts of glacial acetic acid, propionic acid, butyric acid, hexanoic acid, and the like. Both the cracking catalyst and the trimerization catalyst are present throughout the conversion of the silylorganocarbamate to silylisocyanurate in the process of U.S. Pat. No. 5,218,133. Due to toxicity and/or environmental considerations, the foregoing aluminum-containing and tin-containing cracking catalysts, if solid, must be separated from the liquid product stream or, if liquid, will remain dissolved in the product stream where they can cause instabilities such as an increase in color and/or adversely affect the end use(s) of the product silylisocyanurate.